The present invention concerns in a general manner the field of continuous electric power supply circuits, in particular for timepieces.
Some timepieces comprise in fact a solar cell, or an other intermittent electrical source, which provides the necessary electrical energy to an electric movement and/or to electronic circuits, for example, for the regulation of the movement. Unfortunately, when the timepieces is not illuminated, the photovoltaic cell does not anymore provide electricity. To avoid the interruption of the movement or the functioning of the electronic circuit, it is necessary to provide an energy storing device, such as a capacitor, which is connected between the solar cell and the circuit/movement in question for storing the energy provided by the solar cell when it is producing such. This energy storing device is then used as a direct power supply source of the circuit/movement.
However, the supply voltage needed to operate several circuits/movements is often very low. This is in particular the case in low power circuits in the field of watches. Given the fact that the quantity of energy E which may be stored by using such an energy storing device is a function of the supply voltage U which it provides (for a capacitor, for example, this function is given by the formula E=1/2.C.U.sup.2 in which C is the capacity of the capacitor), this stored quantity of energy is limited. Consequently, the functioning of the circuit/movement can only be assured for a reduced period of time after the end of the illumination of the solar cell.
To overcome these inconveniences, it would be possible to add a secondary or a backup power supply in such a supply circuit. This backup supply may be obtained by an electrical battery or even by an electrochemical accumulator which stores energy, such as a nickel-cadmium (Ni-Cd) battery and could be used as a supply source in the case that the energy stored by an energy storing source is exhausted. However, these components have the inconvenience of being large and of having a limited life-time.